1. Field of the Invention
The present disclosure relates to display field, more particular to a driving method of display panels.
2. Discussion of the Related Art
FIG. 1 illustrates a pixel driving circuit, including three transistors and one capacitor (3T1C), of a conventional organic light emitting diode (OLED). “Data” indicates data driving signals, “Gate1” indicates charging scanning signals configured to control a transistor T1 to charge “A” point. “Gate2” indicates discharging scanning signals configured to control a transistor T3 to drive the “A” point to discharge. “OVDD” indicates constant voltage signals. “OVSS” indicates an output voltage of the OLED. “Vref' indicates a reference voltage.
With respect to the pixel driving circuit, a threshold voltage Vth of a transistor T2 may drift after a long-time operation, resulting in a non-uniform brightness of a display panel. Conventionally, a pulse-width modulation (PWM) driving mode is provided to improve the image-display of the OLED. The PWM driving mode may eliminate the non-uniform brightness problem of the display panel when comparing with an analog driving mode.
FIG. 2 is a schematic view illustrating an arrangement of sub-fields in a next frame in the conventional PWM driving mode. FIG. 2 is an example of an eight-bit (digital) driving mode, wherein X-axis indicates the time and Y-axis indicates scanning time of scanning lines. One frame may include a plurality of sub-fields SF, wherein each of the sub-fields has the same time period. The brightness of grayscale value may be displayed by a digital voltage (two Gamma voltages) via controlling charging time of the sub-field SF in conjunction with a principle of time integration of human perception of brightness.
Specifically, by controlling the charging and discharging time, each of the sub-fields SF within a pixel may have different emission time. Taking one frame divided into eight sub-fields as an example. The emission time is determined according to the weight, such as 1:1/2:1/4:1/8:1/16:1/32:1/64:1/128, to generate PWM emission signals. Although, the hardware is easy to implement in the PWM driving mode, the pixels do not illuminate at most of the time, resulting in low-brightness. For example, a ratio of the illumination time with respect to the pixel within one frame under 255 grayscale values (eight sub-fields illuminates at the same time) is at about 25%. That is, the brightness is merely 25% of the 255 grayscale values driven by analog potentials. Therefore, the brightness of the panel will be extremely dark when driven by PWM driving mode.